System and method for monitoring thermal ablation using radiofrequency echoes

Abstract

Radiofrequency energy emitted from and reflected back toward a thermal ablation probe may be used to detect a gradual dissolution of a reflective interface between a tumor and surrounding healthy tissue as the ablation zone passes through this interface providing a real-time guidance with respect to the progress of ablation.

What we claim is: 
     
       1. An ablation apparatus comprising:
 a probe adapted for percutaneous insertion of a distal end of the probe through tissue for disruption of a tumor within the tissue; 
 a transmitting circuit adapted to communicate with the probe when the latter is inserted into tissue to transmit a measurement radiofrequency signal from the distal end of the probe; 
 a receiving circuit adapted to communicate with the probe to receive an echo of the measurement radio frequency signal caused by dielectric boundaries; and 
 a processing circuit including an electronic computer configured to execute a program stored in a non-transient medium and configured to operate to process the echo during ablative procedure to track a boundary of the disruption by 
 (i) using the echo to develop a tumor-free echo modeling the tissue under ablation to provide an ablation boundary echo but not an echo from a tumor-healthy tissue boundary, 
 (ii) subtracting the tumor-free echo from the echo to provide a tumor-healthy tissue echo, and 
 (iii) using the tumor-healthy tissue echo to provide an output indicating passage of an ablation boundary past a tumor-healthy tissue boundary. 
 
     
     
       2. The ablation apparatus of  claim 1  wherein the transmitting circuit is adapted to also transmit an ablation radio frequency signal from the distal end of the probe for thermal ablation of tissue at the distal end of the probe. 
     
     
       3. The ablation apparatus of  claim 2  wherein the transmitting circuit is adapted to alternate between an ablation radiofrequency signal and a measurement radiofrequency signal. 
     
     
       4. The ablation apparatus of  claim 1  wherein the processing circuit is configured to further operate to determine distance of a source of the echo from the probe. 
     
     
       5. The ablation apparatus of  claim 4  wherein the determination of distance uses at least one of time domain reflectometry and frequency domain reflectometry. 
     
     
       6. The ablation apparatus of  claim 1  wherein the tumor-free echo is determined by fitting of echo models to the echo data, the echo models based on echoes in ablated tissue in the absence of a tumor. 
     
     
       7. The ablation apparatus of  claim 1  wherein the output from the processing circuit is further configured to operate to provide a display indicating a change in the strength of echo from the dielectric boundary between the tumor and tissue. 
     
     
       8. The ablation apparatus of  claim 1  wherein the output is adapted to control the thermal ablation applied to the tissue. 
     
     
       9. The ablation apparatus of  claim 8  wherein the output is adapted to determine a time of continued ablation after the dielectric boundary between the tumor and tissue is fully decreased. 
     
     
       10. The ablation apparatus of  claim 1  wherein the transmitting circuit is a microwave transmitter. 
     
     
       11. The ablation apparatus of  claim 1  wherein the probe is a microwave antenna. 
     
     
       12. A monitoring system for in vivo tumor disruption comprising:
 a microwave transmitter adapted to connect to an antenna for percutaneous insertion into a tumor within tissue, the microwave power source adapted to provide a low power microwave output that sweeps through a frequency range below a power level providing thermal ablation; 
 a microwave receiver adapted to receive reflected power of the low power microwave output into the antenna; and 
 an electronic computer configured to execute a program stored in a non-transient medium to communicate with the microwave receiver and to analyze the reflected power during ablative procedure to develop a tumor-free reflected power associated with the tissue under ablation absent a tumor-healthy tissue boundary and subtract the tumor-free reflected power from the reflected power to provide an output indicating a decrease in reflected power associated with the boundary between the tumor and tissue indicating progress of the tumor disruption process. 
 
     
     
       13. The monitoring system of  claim 12  wherein the microwave power source further provides a high-power radiofrequency output for ablation of the tumor through radiofrequency energy coupled to the tumor out of the antenna. 
     
     
       14. The monitoring system of  claim 12  wherein the microwave transmitter provides a port adapted to communicate with a tissue disrupting power source to provide interleaved periods of application of tissue disrupting power to the tumor and to receive reflected power. 
     
     
       15. A method of performing thermal ablation using an ablation apparatus having:
 a probe adapted for percutaneous insertion of a distal end of the probe through tissue for disruption of a tumor within the tissue; 
 a transmitting circuit adapted to communicate with the probe when the latter is inserted into tissue to transmit a measurement radiofrequency signal from the distal end of the probe; 
 a receiving circuit adapted to communicate with the probe to receive an echo of the measurement radio frequency signal caused by dielectric boundaries; and 
 a processing circuit including an electronic computer configured to execute a program stored in non-transient medium and configured to operate to process the echo during thermal ablation to track a boundary of the disruption by (i) using the echo to develop a tumor-free echo modeling the tissue under ablation to provide an ablation boundary echo but not an echo from a tumor-healthy tissue boundary, (ii) subtracting the tumor-free echo from the echo to provide a tumor-healthy tissue echo, and (iii) using the tumor-healthy tissue echo to provide an output indicating passage of an ablation boundary past a tumor-healthy tissue boundary; 
 the method comprising the steps of: 
 inserting a probe percutaneously into tissue so that a distal end of the probe is received within a tumor within the tissue; 
 treating the tumor using the probe; 
 contemporaneously with the treatment, transmitting a measurement radiofrequency signal from the distal end of the probe; 
 analyzing a received echo of the measurement radio frequency signal caused by dielectric boundaries within the tissue; and 
 outputting an indication of a decrease in a dielectric boundary between the tumor and the tissue associated with thermal ablation of the tumor based on the analyzing of the received echo.